Our studies of membrane energetics have centered around an examination of so-called unc mutants of Escherichia coli. The mutants are altered in the Ca, Mg ions ATPase complex and are defective in their ability to couple energy from electron transport to energy-dependent processes such as oxidative phosphorylation, active transport, and transhydrogenase activity. We have attempted to define these mutants biochemically and genetically. Other aspects of this general project have employed naturally occurring fluorescent fatty acids as probes of the energy state of the membrane. The fluorescence intensity of parinaric acid added to intact cells is strongly dependent on the energy state of the cells. Furthermore, this probe, which can be biosynthetically incorporated into E. coli phospholipids, detects changes in the physical state of the membrane. BIBLIOGRAPHIC REFERENCES: Sklar, L.A., Hudson, B. S., and Simoni, R. D. Conjugated polyene fatty acids as fluorescent probes: Synthetic phospholipid membrane studies. Biochemistry 16, 819. 1977. Tecoma, E., Skler, L. A., Simoni, R. D., and Hudson, B.S. Conjugated polyene fatty acids as fluorescent membrane probes: Incorporation of parinaric acid by Escherichia coli and studies of phase transitions. Biochemistry 16, 829. 1977.